1. Field of the Invention
The present invention relates to a crane including a boom provided with a device for attaching/detaching crawlers and the like by itself.
2. Description of the Related Art
In general, large crawler cranes are difficult to transport the entire body thereof together, and are therefore divided into a plurality of blocks to be transported individually by trailers. Then, the blocks are assembled together at the scene. In the assembling/disassembling process, if an additional crane is not available, components are assembled/disassembled using their own equipment.
In FIGS. 5 and 6, a hoisting rope 9 pulled out from a hoisting winch 8 extends along a path through a first sheave 5, a second sheave 6, a hook sheave 11 of a hanging hook 10, and a third sheave 7, in that order. A rope end 9a of the hoisting rope 9 is attached to a bracket 12 provided on a lower boom 4 at a position under the first sheave 5.
A crawler 2 placed on a trailer (not shown) is lifted and moved closer to a lower traveling body 1 by driving the hoisting winch 8 while the crawler 2 is attached to the hanging hook 10 with a hanging rope 14 and raising the lower boom 4. Then, the crawler 2 is assembled to the lower traveling body 1.
In this case, since the second and third sheaves 6 and 7 are arranged vertically on a front side of the lower boom 4, the following problems occur:
(i) Lifting Height
Since the hoisting rope 9 from the first sheave 5 extends along the above-described path, the hanging hook 10 hangs in a longitudinal orientation such that side surfaces in the width direction of the hanging hook 10 face the lower boom 4, as shown in FIG. 5. Therefore, the hook 10 easily approaches and interferes with the lower boom 4. As a result, the hook 10 cannot be lifted high, that is, the lifting height cannot be increased, which is disadvantageous in the self-attaching/detaching operation.
(ii) Attachment/Detachment of Rope End 9a 
The rope end 9a is attached to the bracket 12 at a position below the first sheave 5 (position nearer to the base end of the lower boom 4). Accordingly, the attachment position is shifted from the top end of the lower boom 4 toward the base end thereof (out of reach of a hand from the top end). Therefore, as shown in FIG. 6, a worker W must get inside the narrow lower boom 4 to attach/detach the rope end 9a of the hoisting rope 9. The task of attaching/detaching the rope end 9a is cumbersome, and there is also a safety hazard. Since the worker W can reach a top end portion of the lower boom 4 from the outside (from the front when the lower boom 4 is laid down as shown in FIG. 6) without getting inside the lower boom 4, the rope end 9a may be attached to the top end portion of the lower boom 4. However, in this case, the rope end 9a is obstructed by a rope segment between the first and second sheaves 5 and 6, and cannot be attached at a position above this rope segment, that is, a position nearer to the top end of the lower boom 4.
Japanese Unexamined Patent Application Publication No. 6-16388 discloses a structure in which, in comparison with the structure shown in FIG. 6, only the second sheave 6 is provided on the front side of the lower boom 4. In this structure, the hoisting rope 9 extends through the first and second sheaves 5 and 6 and the hook sheave 11, in that order, and the rope end 9a is attached to the front side of the lower boom 4 (bottom side in FIG. 6) at a position under the second sheave 6. However, the problems of above items (i) and (ii) cannot be solved by this structure.